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Wellbore annular pressure control system and method using gas lift in drilling fluid return line

  • US 9,376,875 B2
  • Filed: 04/29/2013
  • Issued: 06/28/2016
  • Est. Priority Date: 04/27/2012
  • Status: Active Grant
First Claim
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1. A system comprising:

  • a drill string extending into a wellbore below a bottom of a body of water;

    a primary pump for selectively pumping a drilling fluid through the drill string and into an annular space created between the drill string and the wellbore;

    a riser extending from a top of the wellbore to a platform on a surface of the body of water;

    a fluid discharge conduit in fluid communication with the riser;

    a controllable orifice choke coupled to the discharge conduit;

    a fluid return line extending from the choke to the platform;

    a source of compressed gas coupled to the fluid return line at a selected depth below the surface of the body of water;

    a separator coupled to the fluid return line;

    a flow meter coupled to a gas discharge end of the separator; and

    a controller configured to receive an input signal from the flow meter and configured to compare a flow rate of gas measured by the flow meter to a flow rate of gas pumped into the fluid return line.

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